1. Field of the Invention
This invention pertains to a spring tooth harrow, to a spring tooth for a harrow, and to an attachment clip for securing a spring tooth to a harrow.
2. The Prior Art
Spring tooth harrows were devised many years ago. The first designs had the helical spring coils mounted around a tubular structural member. This is an excellent and very strong method of devising a harrow and of mounting a helical coil harrow tooth. Unfortunately, if you brake a tooth, you must dis-assemble the entire harrow to replace the tooth. The customers comprising the harrow marketplace found this unacceptable.
Therefore, the spring tooth was mounted on the outside of the harrow frame so it could be replaced when broken, and so the harrow frames could be fabricated without teeth, and teeth added by the retailers or farmers.
The most commonly used cross-members in harrows are tubes and angle iron sections. The harrow teeth are fastened to these sections. The tube does not lend itself to advantagous securement of a helical coil spring tooth, if the helical coil is not around the tube. The angle iron is easy to fasten to, but it has proven very difficult to effectively fasten and mount a spring tooth to and retain strength and avoid breakage.
The problem is that the tooth has to be secured in both the fore-aft axis and the side-to-side axis. As the harrow is pulled over large clumps of earth, rocks, debris and the like, the teeth tend to be bent both rearward and forward, and also to either side. If the teeth turn sideways, the harrow will no longer work. It is very difficult to mount spring teeth without developing stress concentrations in the mounting eye or lug of the spring tooth. More often than not the spring tooth breaks in the mounting lug. Then the fastener will break in some instances. An example of this type of harrow is in C. B. Blair, U.S. Pat. No. 3,976,145.
The most recent and closest known example of prior art is a spring tooth harrow utilizing an angle iron frame to which a spring tooth having a helical coil spring is attached. The angle iron has a lower flange in which an aperture is pierced. A slot is notched in the lower edge of the angle lower flange. The tooth has a U-shaped lug in which the outboard leg of the U-shape has a forwardly bent toe that goes into the notch. A bolt and washer secure the lug to the angle iron. This device weakens the angle iron and contributes to bent frames, and gives excessive stress concentration in the lug because the mounting footprint is too small, and experiences too much lug breakage or tooth bending. This harrow is subject of H. L. Kovar, U.S. Pat. No. 3,710,872 of Jan. 16, 1973.